Well to me it sounds like you have a bigger.job than just covering up...well if you want tonrepair and notjust wait for it to blow.

First...it has to be dry. If the box is not lose you might get away with drilling down around it.
Personally I would use epoxy with filler to bond. If I had to take out the box I would give the board to an expert...drill fill..might want to add some glass on top...so a lot of sanding. The point is you have to make the box bond with the foam...make sure everything is dry.

i m having it directly to the sun so it "bakes" from inside.the box is moving a bit(about 2mm) in and out but only in the damage point.So you say drilling a few holes of 3,5mm and injecting epoxy or 3M 5200 inside it will be ok?

Thanks for the photo
Step 1 remove fin sand off the paint covering all the box, so you can see the glass 25mm all round
Step 2 mask off the bottom you have sanded and the box spin it over bottom down
Step 3 drill one hole in the deck rail over the damaged box but not into the box and not bigger than the syringe neck ( a tight fit )
Step 4 epoxy mixed with glass bubbles using a syringe inject the hole approximately 5ml. more than 5ml you run the risk of over heating when the resin goes off

This is to reattach the box back to the deck and to stiffen up the damage under the box

When you have done that and the epoxy has gone hard remove the masking tape from the bottom
Then re glass mat 80/ 100 grams over the box then sand back fill and flat off and spray with paint

Hope this helps

Ps check the old box is not split in side if so you will have to replace it

chipmunk wrote:Thanks for the photo
Step 1 remove fin sand off the paint covering all the box, so you can see the glass 25mm all round
Step 2 mask off the bottom you have sanded and the box spin it over bottom down
Step 3 drill one hole in the deck rail over the damaged box but not into the box and not bigger than the syringe neck ( a tight fit )
Step 4 epoxy mixed with glass bubbles using a syringe inject the hole approximately 5ml. more than 5ml you run the risk of over heating when the resin goes off

This is to reattach the box back to the deck and to stiffen up the damage under the box

When you have done that and the epoxy has gone hard remove the masking tape from the bottom
Then re glass mat 80/ 100 grams over the box then sand back fill and flat off and spray with paint

Hope this helps

Ps check the old box is not split in side if so you will have to replace it